1. Field of the Invention
This invention relates to polymeric compositions comprising fluoropolyers.
2. Introduction to the Invention
Fluoropolymers are well known and are useful in a broad range of applications. Some fluoropolymers can be melt-shaped, including for example polyvinylidene fluoride and copolymers of tetrafluoroethylene and ethylene, hexafluoropropylene, or a perfluorinated vinyl ether. These fluoropolymers have been used extensively for electrical insulation, particularly as melt-extruded jackets around conductors, and exhibit a valuable combination of physical and electrical properties. They have also been used in conductive polymer compositions which comprise the fluoropolymer and carbon black or another conductive filler dispersed therein. However, other fluoropolymers, in particular polytetrafluoroethylene (PTFE), which have very high crystallinity, also have such high molecular weights that they cannot be melt-shaped. This makes them difficult and expensive to process, and has severely restricted their use, despite the fact that in some respects they offer important advantages over the melt-shapeable fluoropolymers, in particular one or more of good elongation, high melting point and low loss tangent at high frequencies. Attempts have been made to produce similar polymers which retain these advantages but have relatively low molecular weights so that they can be melt-extruded. However, such polymers have such poor mechanical properties that they are of little practical value. For example, PTFE can be irradiated to produce a material which retains the crystallinity of the original polymer but has a relatively low molecular weight, but melt extrusion of this material results in products which are extremely brittle (see U.S. Pat. No. 3,838,030, Kagiya et al, the disclosure of which is incorporated herein by reference).
Conductive polymer compositions, including such compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Reference may be made, for example, to U.S. Pat. Nos. 2,952,761; 2,978,665; 3,243,753; 3,351,882; 3,571,777; 3,757,086; 3,793,716; 3,823,217; 3,858,144; 3,861,029; 3,950,604; 4,017,715; 4,072,848; 4,085,286; 4,117,312; 4,177,376; 4,177,446; 4,188,276; 4,237,441; 4,242,573; 4,246,468; 4,250,400; 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139; 4,459,473, 4,481,498, 4,473,450, and 4,502,929; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 now abandoned, published as German OLS No. 1,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al), published as European Application No. 38,718; 141,988 (Fouts et al), published as European Application No. 38,718,141,989 (Evans), published as European Application No. 38,713, 141,991 (Fouts et al), published as European Application No. 38,714, 150,909 (Sopory), published as UK Application No. 2,076,106A, 184,647 (Lutz), 250,491 (Jacobs et al) published as European Application No. 63,440, 272,854 and 403,203 (Stewart et al), published as European Patent Application No. 67,679, 274,010 (Walty et al), 300,709 and 423,589 (Van Konynenburg et al), published as European Application No. 74,281, 369,309 (Midgley et al), 483,633 (Wasley), 493,445 (Chazan et al), published as European Application No. 128,664, 606,033 (Leary et al), published as European Application No. 119,807, 509,897, 598,048, 603,485 and 618,109 (Masia et al), published as European Application No. 84304502.2, 524,482 (Tomlinson et al), published as European Application No. 84305584.9, 534,913 (McKinley), 535,449 (Cheng et al) published as European Application No. 84306456.9, 552,649 (Jensen et al), published as European Application No. 8407984.9, 573,099 (Batliwalla et al), 904,736, published as UK Patent Nos. 1,470,502 and 1,470,503, 628,945 (Carlomagno), 650,918, 650,919, 650,920 and 663,014 (Batliwalla et al), and in the commonly assigned patent applications filed Mar. 14, 1985, by Ratell, Ser. Nos. 711,908 filed on Mar. 14, 1985, now U.S. Pat. No. 4,647,896 and 711,907 filed on Mar. 14, 1985 now U.S. Pat. No. 4,647,894 (MP1016 and MP1021), Carlomagno, Ser. No. 711,790 filed on Mar. 14, 1985, now U.S. Pat. No. 4,685,025 (MP0991), Au et al, Ser. No. 711,910 filed on Mar. 14, 1985, now U.S. Pat. No. 4,724,417 (MP1044), Deep et al, Ser. No. 711,909 filed on Mar. 14, 1985, now U.S. Pat. No. 4,774,024 (MP1022). The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.